THE LAST CHAPTER ON CHLOROFLUOROCARBON PHOTOOXIDATION PROCESSES - FORMATION AND DISSOCIATION OF FC(O)ONO

The key features of the potential energy surface of FC(O)ONO and its FC(O)NO2 isomer have been determined using ab initio molecular orbital theory. This species, which may be regarded as the NO adduct of the FC(O)O radical, is postulated to be an intermediate in the atmospheric degradation of chlorofluorocarbons. Hartree-Fock (HF) and second-order Moller-Plesset perturbation theory (MP2) are used to characterize the structure and vibrational frequencies of two FC(O)ONO chain conformers and two higher energy isomers, including a stable cyclic species whose structure can be represented as FN[(O)(O)]C=O. Relative energies are determined using MP4 and QCISD(T) (quadratic configuration interaction with single, double, and triple excitations) methods. Transition states are found connecting the two FC(O)ONO chain conformers to each other, to FC(O)NO2, and to stable degradation products. The exothermicity of formation of FC(O)ONO by any pathway is more than sufficient to overcome the barrier to formation of FNO + CO2, the most exothermic species on the entire potential energy surface. Thus, the reaction of FC(O)O-x radicals with NOx radicals terminates chlorofluorocarbon photooxidation by converting FC(O)O, radicals to CO2 and FNO, which is suggested as a hitherto undetected fluorine reservoir species.